The recognition of digital services offered by a network is standardized by DVB in the context of a satellite, cable or digital terrestrial transmission network. This standard is described in the document “Digital Video Broadcasting (DVB); Specification for Service Information (SI) in DVB Systems”, published by the ETSI (European Telecommunication Standards Institute) under number ETSI EN 300 468. This document describes a set of tables containing information on the network, on the frequencies at which the data streams containing the services are transmitted, on the services offered, etc. The reader can also refer to the document “MPEG-2 system—ISO IEC 13818-1” for a definition of the transport stream format. A transport stream therefore contains audio data, video data, ancillary data such as subtitles, teletext or interactive applications in the form of elementary streams, and minimum mandatory signalling tables used to organize the content as a Network Information Table (NIT) enabling the other transport streams on the network to be found, the Program Association Table (PAT) and the Program Map Table (PMT) among others. These tables are multiplexed in the transport stream, the receiver being configured with the data needed to connect to a first stream enabling it to receive these tables and to construct, from their content, a database containing the list of services offered by the network and the connection data needed to receive them.
With the expansion of digital bidirectional data networks, in particular the Internet, and above all the roll-out of high speed services, the technical capability to transmit audiovisual digital services over this type of network is now available. Also, private, high bit rate IP networks are being developed, for both corporate and home use. Within this context, DVB is working to standardize the broadcasting of DVB services over the IP networks. A working group called DVB-IPI (Internet Protocol Infrastructure) is in the process of finalizing a specification concerning the transport of DVB digital services over an IP network and, more specifically, the recognition of these services. The proposal as currently envisaged is described in the document “DVB-IP Phase 1 Handbook” under reference IPI2003-227. The solution, as currently envisaged by the working group, is oriented towards a separation between the broadcasting of the services in the form of transport streams containing a single DVB service on the one hand and the information describing these services, available in the form of XML (eXtensible Markup Language) files accessible to the terminals on request, for example. The HTTP (Hyper Text Transport Protocol) can, for example, be used to retrieve these files. This solution seems natural because it exploits the bidirectional nature of the IP connection, as contrasted with satellite transmission, for example. In practice, standards such as DVB have been designed from the perspective of a unidirectional transmission network requiring all the information likely to be useful to a receiver to be transmitted permanently. The bidirectional nature of the networks considered means that a distinction can be drawn between the information useful for decoding the audiovisual service and the service description information. These two types of information that are conventionally included in a DVB stream are not used synchronously by the receiver. Their transmission over the network may therefore be separated, so providing a bandwidth saving by the fact that the signalling information is transmitted only on request and not permanently in the audio and video channel. Furthermore, the provision of information on an IP type network via HTTP servers in the form of XML data files is the predominant solution broadly adopted on this type of network.
However, this solution makes it necessary to develop a set of tools for generating and managing the servers offering this signalling information in XML format. In fact, at the present time, content broadcasters have a controlled infrastructure for transmitting MPEG-2 DVB services via satellite or cable. Since the adoption of this new signalling system means that new tools have to be developed in parallel with the existing system, operators have to make an investment and take a risk. Furthermore, terminals do not currently incorporate the tools needed to analyse this information, such as an XML analyser, for example. The incorporation of such tools in an inexpensive receiver may prove difficult and even impossible depending on the hardware resources available, such as processor power or memory.